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Reasons for a Miscarriage in First 12 to 24 Weeks of Pregnancy

Early and Late Miscarriages

Miscarriage is the lay term for what is medically referred to as a spontaneous abortion. It refers to the loss of a pregnancy in the early stages, usually prior to 20 weeks or before the the fetus reaches 500 grams, where it is not viable for the fetus to exist outside of the uterus. It is also known as early pregnancy loss before 12 weeks although this term may also include an induced abortion where a woman purposefully undergoes any medical or surgical treatment to end the pregnancy.

Late miscarriages occur after the first 12 weeks and before the first 24 weeks of pregnancy. Up to 20% of pregnancies (2 out of 10) end in miscarriage and in the majority of cases this occurs in the first trimester (12 weeks). However, miscarriage is mainly a once off occurrence and a woman may go on to have a health full term pregnancy afterwards. Less than 1 out of 100 women will experience 2 to 3 consecutive miscarriages.

There is no guarantee that every pregnancy will go on to full term despite the best efforts of the mother, caregivers and medical professionals. While some factors such as advancing maternal age, generally over 35 years, is known to be associated with a greater risk of miscarriage, there is no sure way of knowing at the outset whether a pregnancy will end with the delivery of a healthy baby or in a miscarriage. Nevertheless, if a miscarriage happens more than once consecutively, it needs to be investigated further.

Why do women miscarry?

The exact reason for a miscarriage cannot always be determined. Intensive investigation is warranted in the event of recurrent spontaneous abortions. Some of the possible causes of a miscarriage includes :

Genetic abnormalities, also known as chromosomal abnormalities, are the most common causes of miscarriage with most occurring within the first trimester and less frequently before 24 weeks.

Various factors, sometimes unknown, may be teratogenic (causes embryo malformation) or mutagenic (causes gene mutation). This can at times be associated with lifestyle factors such as cigarette smoking, alcohol consumption and illicit drug use.

Structural problems of the uterus, cervix and endocervical canal. This includes uterine fibroids.

Previous uterine surgery can cause adhesions (scar tissue) which may also complicate the pregnancy and lead to miscarriage. This is known as Asherman’s syndrome. Certain medication may also be a causative factor particularly in an unplanned pregnancy. Surgical and medical factors are known as iatrogenic causes. Read more on drugs that affect pregnancy.

Infections such as rubella (German measles), toxoplasmosis and Listeria infection.

Chronic diseases particularly endocrine and gynecological disorders such as polycystic ovary syndrome, thyroid disorders, uncontrolled diabetes mellitus, Cushing syndrome and corpus lutem deficiency which is more often acute. Other conditions such as kidney disease, systemic lupus erythematosus (SLE), severe hypertension, sickle cell anemia and antiphospholipid-antibody syndrome may also be associated with a miscarriage.